drm/ttm: add a way to bo_wait for either the last read or last write

Sometimes we want to know whether a buffer is busy and wait for it (bo_wait).
However, sometimes it would be more useful to be able to query whether
a buffer is busy and being either read or written, and wait until it's stopped
being either read or written. The point of this is to be able to avoid
unnecessary waiting, e.g. if a GPU has written something to a buffer and is now
reading that buffer, and a CPU wants to map that buffer for read, it needs to
only wait for the last write. If there were no write, there wouldn't be any
waiting needed.

This, or course, requires user space drivers to send read/write flags
with each relocation (like we have read/write domains in radeon, so we can
actually use those for something useful now).

Now how this patch works:

The read/write flags should passed to ttm_validate_buffer. TTM maintains
separate sync objects of the last read and write for each buffer, in addition
to the sync object of the last use of a buffer. ttm_bo_wait then operates
with one the sync objects.

Signed-off-by: Marek Olšák <maraeo@gmail.com>
Reviewed-by: Jerome Glisse <jglisse@redhat.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>

drivers/gpu/drm/nouveau/nouveau_bo.c

@@ -1104,7 +1104,8 @@ nouveau_bo_vma_del(struct nouveau_bo *nvbo, struct nouveau_vma *vma)
 	if (vma->node) {
 		if (nvbo->bo.mem.mem_type != TTM_PL_SYSTEM) {
 			spin_lock(&nvbo->bo.bdev->fence_lock);
-			ttm_bo_wait(&nvbo->bo, false, false, false);
+			ttm_bo_wait(&nvbo->bo, false, false, false,
+				    TTM_USAGE_READWRITE);
 			spin_unlock(&nvbo->bo.bdev->fence_lock);
 			nouveau_vm_unmap(vma);
 		}

drivers/gpu/drm/nouveau/nouveau_gem.c

@@ -589,7 +589,8 @@ nouveau_gem_pushbuf_reloc_apply(struct drm_device *dev,
 		}
 
 		spin_lock(&nvbo->bo.bdev->fence_lock);
-		ret = ttm_bo_wait(&nvbo->bo, false, false, false);
+		ret = ttm_bo_wait(&nvbo->bo, false, false, false,
+				  TTM_USAGE_READWRITE);
 		spin_unlock(&nvbo->bo.bdev->fence_lock);
 		if (ret) {
 			NV_ERROR(dev, "reloc wait_idle failed: %d\n", ret);
@@ -825,7 +826,7 @@ nouveau_gem_ioctl_cpu_prep(struct drm_device *dev, void *data,
 	nvbo = nouveau_gem_object(gem);
 
 	spin_lock(&nvbo->bo.bdev->fence_lock);
-	ret = ttm_bo_wait(&nvbo->bo, true, true, no_wait);
+	ret = ttm_bo_wait(&nvbo->bo, true, true, no_wait, TTM_USAGE_READWRITE);
 	spin_unlock(&nvbo->bo.bdev->fence_lock);
 	drm_gem_object_unreference_unlocked(gem);
 	return ret;

drivers/gpu/drm/radeon/radeon_cs.c

@@ -80,6 +80,7 @@ int radeon_cs_parser_relocs(struct radeon_cs_parser *p)
 			p->relocs[i].lobj.wdomain = r->write_domain;
 			p->relocs[i].lobj.rdomain = r->read_domains;
 			p->relocs[i].lobj.tv.bo = &p->relocs[i].robj->tbo;
+			p->relocs[i].lobj.tv.usage = TTM_USAGE_READWRITE;
 			p->relocs[i].handle = r->handle;
 			p->relocs[i].flags = r->flags;
 			radeon_bo_list_add_object(&p->relocs[i].lobj,

drivers/gpu/drm/radeon/radeon_object.h

@@ -130,7 +130,7 @@ static inline int radeon_bo_wait(struct radeon_bo *bo, u32 *mem_type,
 	if (mem_type)
 		*mem_type = bo->tbo.mem.mem_type;
 	if (bo->tbo.sync_obj)
-		r = ttm_bo_wait(&bo->tbo, true, true, no_wait);
+		r = ttm_bo_wait(&bo->tbo, true, true, no_wait, TTM_USAGE_READWRITE);
 	spin_unlock(&bo->tbo.bdev->fence_lock);
 	ttm_bo_unreserve(&bo->tbo);
 	return r;

drivers/gpu/drm/ttm/ttm_bo.c

@@ -498,7 +498,7 @@ static void ttm_bo_cleanup_refs_or_queue(struct ttm_buffer_object *bo)
 	int ret;
 
 	spin_lock(&bdev->fence_lock);
-	(void) ttm_bo_wait(bo, false, false, true);
+	(void) ttm_bo_wait(bo, false, false, true, TTM_USAGE_READWRITE);
 	if (!bo->sync_obj) {
 
 		spin_lock(&glob->lru_lock);
@@ -566,7 +566,8 @@ static int ttm_bo_cleanup_refs(struct ttm_buffer_object *bo,
 
 retry:
 	spin_lock(&bdev->fence_lock);
-	ret = ttm_bo_wait(bo, false, interruptible, no_wait_gpu);
+	ret = ttm_bo_wait(bo, false, interruptible, no_wait_gpu,
+			  TTM_USAGE_READWRITE);
 	spin_unlock(&bdev->fence_lock);
 
 	if (unlikely(ret != 0))
@@ -725,7 +726,8 @@ static int ttm_bo_evict(struct ttm_buffer_object *bo, bool interruptible,
 	int ret = 0;
 
 	spin_lock(&bdev->fence_lock);
-	ret = ttm_bo_wait(bo, false, interruptible, no_wait_gpu);
+	ret = ttm_bo_wait(bo, false, interruptible, no_wait_gpu,
+			  TTM_USAGE_READWRITE);
 	spin_unlock(&bdev->fence_lock);
 
 	if (unlikely(ret != 0)) {
@@ -1072,7 +1074,8 @@ int ttm_bo_move_buffer(struct ttm_buffer_object *bo,
 	 * instead of doing it here.
 	 */
 	spin_lock(&bdev->fence_lock);
-	ret = ttm_bo_wait(bo, false, interruptible, no_wait_gpu);
+	ret = ttm_bo_wait(bo, false, interruptible, no_wait_gpu,
+			  TTM_USAGE_READWRITE);
 	spin_unlock(&bdev->fence_lock);
 	if (ret)
 		return ret;
@@ -1692,34 +1695,83 @@ out_unlock:
 	return ret;
 }
 
+static void ttm_bo_unref_sync_obj_locked(struct ttm_buffer_object *bo,
+					 void *sync_obj,
+					 void **extra_sync_obj)
+{
+	struct ttm_bo_device *bdev = bo->bdev;
+	struct ttm_bo_driver *driver = bdev->driver;
+	void *tmp_obj = NULL, *tmp_obj_read = NULL, *tmp_obj_write = NULL;
+
+	/* We must unref the sync obj wherever it's ref'd.
+	 * Note that if we unref bo->sync_obj, we can unref both the read
+	 * and write sync objs too, because they can't be newer than
+	 * bo->sync_obj, so they are no longer relevant. */
+	if (sync_obj == bo->sync_obj ||
+	    sync_obj == bo->sync_obj_read) {
+		tmp_obj_read = bo->sync_obj_read;
+		bo->sync_obj_read = NULL;
+	}
+	if (sync_obj == bo->sync_obj ||
+	    sync_obj == bo->sync_obj_write) {
+		tmp_obj_write = bo->sync_obj_write;
+		bo->sync_obj_write = NULL;
+	}
+	if (sync_obj == bo->sync_obj) {
+		tmp_obj = bo->sync_obj;
+		bo->sync_obj = NULL;
+	}
+
+	clear_bit(TTM_BO_PRIV_FLAG_MOVING, &bo->priv_flags);
+	spin_unlock(&bdev->fence_lock);
+	if (tmp_obj)
+		driver->sync_obj_unref(&tmp_obj);
+	if (tmp_obj_read)
+		driver->sync_obj_unref(&tmp_obj_read);
+	if (tmp_obj_write)
+		driver->sync_obj_unref(&tmp_obj_write);
+	if (extra_sync_obj)
+		driver->sync_obj_unref(extra_sync_obj);
+	spin_lock(&bdev->fence_lock);
+}
+
 int ttm_bo_wait(struct ttm_buffer_object *bo,
-		bool lazy, bool interruptible, bool no_wait)
+		bool lazy, bool interruptible, bool no_wait,
+		enum ttm_buffer_usage usage)
 {
 	struct ttm_bo_driver *driver = bo->bdev->driver;
 	struct ttm_bo_device *bdev = bo->bdev;
 	void *sync_obj;
 	void *sync_obj_arg;
 	int ret = 0;
+	void **bo_sync_obj;
 
-	if (likely(bo->sync_obj == NULL))
+	switch (usage) {
+	case TTM_USAGE_READ:
+		bo_sync_obj = &bo->sync_obj_read;
+		break;
+	case TTM_USAGE_WRITE:
+		bo_sync_obj = &bo->sync_obj_write;
+		break;
+	case TTM_USAGE_READWRITE:
+	default:
+		bo_sync_obj = &bo->sync_obj;
+	}
+
+	if (likely(*bo_sync_obj == NULL))
 		return 0;
 
-	while (bo->sync_obj) {
+	while (*bo_sync_obj) {
 
-		if (driver->sync_obj_signaled(bo->sync_obj, bo->sync_obj_arg)) {
-			void *tmp_obj = bo->sync_obj;
-			bo->sync_obj = NULL;
-			clear_bit(TTM_BO_PRIV_FLAG_MOVING, &bo->priv_flags);
-			spin_unlock(&bdev->fence_lock);
-			driver->sync_obj_unref(&tmp_obj);
-			spin_lock(&bdev->fence_lock);
+		if (driver->sync_obj_signaled(*bo_sync_obj, bo->sync_obj_arg)) {
+			ttm_bo_unref_sync_obj_locked(bo, *bo_sync_obj, NULL);
 			continue;
 		}
 
 		if (no_wait)
 			return -EBUSY;
 
-		sync_obj = driver->sync_obj_ref(bo->sync_obj);
+		sync_obj = driver->sync_obj_ref(*bo_sync_obj);
 		sync_obj_arg = bo->sync_obj_arg;
 		spin_unlock(&bdev->fence_lock);
 		ret = driver->sync_obj_wait(sync_obj, sync_obj_arg,
@@ -1730,16 +1782,9 @@ int ttm_bo_wait(struct ttm_buffer_object *bo,
 			return ret;
 		}
 		spin_lock(&bdev->fence_lock);
-		if (likely(bo->sync_obj == sync_obj &&
+		if (likely(*bo_sync_obj == sync_obj &&
 			   bo->sync_obj_arg == sync_obj_arg)) {
-			void *tmp_obj = bo->sync_obj;
-			bo->sync_obj = NULL;
-			clear_bit(TTM_BO_PRIV_FLAG_MOVING,
-				  &bo->priv_flags);
-			spin_unlock(&bdev->fence_lock);
-			driver->sync_obj_unref(&sync_obj);
-			driver->sync_obj_unref(&tmp_obj);
-			spin_lock(&bdev->fence_lock);
+			ttm_bo_unref_sync_obj_locked(bo, *bo_sync_obj, &sync_obj);
 		} else {
 			spin_unlock(&bdev->fence_lock);
 			driver->sync_obj_unref(&sync_obj);
@@ -1763,7 +1808,7 @@ int ttm_bo_synccpu_write_grab(struct ttm_buffer_object *bo, bool no_wait)
 	if (unlikely(ret != 0))
 		return ret;
 	spin_lock(&bdev->fence_lock);
-	ret = ttm_bo_wait(bo, false, true, no_wait);
+	ret = ttm_bo_wait(bo, false, true, no_wait, TTM_USAGE_READWRITE);
 	spin_unlock(&bdev->fence_lock);
 	if (likely(ret == 0))
 		atomic_inc(&bo->cpu_writers);
@@ -1837,7 +1882,7 @@ static int ttm_bo_swapout(struct ttm_mem_shrink *shrink)
 	 */
 
 	spin_lock(&bo->bdev->fence_lock);
-	ret = ttm_bo_wait(bo, false, false, false);
+	ret = ttm_bo_wait(bo, false, false, false, TTM_USAGE_READWRITE);
 	spin_unlock(&bo->bdev->fence_lock);
 
 	if (unlikely(ret != 0))

drivers/gpu/drm/ttm/ttm_bo_util.c

@@ -436,6 +436,8 @@ static int ttm_buffer_object_transfer(struct ttm_buffer_object *bo,
 	atomic_set(&fbo->cpu_writers, 0);
 
 	fbo->sync_obj = driver->sync_obj_ref(bo->sync_obj);
+	fbo->sync_obj_read = driver->sync_obj_ref(bo->sync_obj_read);
+	fbo->sync_obj_write = driver->sync_obj_ref(bo->sync_obj_write);
 	kref_init(&fbo->list_kref);
 	kref_init(&fbo->kref);
 	fbo->destroy = &ttm_transfered_destroy;
@@ -618,20 +620,30 @@ int ttm_bo_move_accel_cleanup(struct ttm_buffer_object *bo,
 	struct ttm_mem_reg *old_mem = &bo->mem;
 	int ret;
 	struct ttm_buffer_object *ghost_obj;
-	void *tmp_obj = NULL;
+	void *tmp_obj = NULL, *tmp_obj_read = NULL, *tmp_obj_write = NULL;
 
 	spin_lock(&bdev->fence_lock);
-	if (bo->sync_obj) {
+	if (bo->sync_obj)
 		tmp_obj = bo->sync_obj;
-		bo->sync_obj = NULL;
-	}
+	if (bo->sync_obj_read)
+		tmp_obj_read = bo->sync_obj_read;
+	if (bo->sync_obj_write)
+		tmp_obj_write = bo->sync_obj_write;
+
 	bo->sync_obj = driver->sync_obj_ref(sync_obj);
+	bo->sync_obj_read = driver->sync_obj_ref(sync_obj);
+	bo->sync_obj_write = driver->sync_obj_ref(sync_obj);
 	bo->sync_obj_arg = sync_obj_arg;
 	if (evict) {
-		ret = ttm_bo_wait(bo, false, false, false);
+		ret = ttm_bo_wait(bo, false, false, false,
+				  TTM_USAGE_READWRITE);
 		spin_unlock(&bdev->fence_lock);
 		if (tmp_obj)
 			driver->sync_obj_unref(&tmp_obj);
+		if (tmp_obj_read)
+			driver->sync_obj_unref(&tmp_obj_read);
+		if (tmp_obj_write)
+			driver->sync_obj_unref(&tmp_obj_write);
 		if (ret)
 			return ret;
 
@@ -655,6 +667,10 @@ int ttm_bo_move_accel_cleanup(struct ttm_buffer_object *bo,
 		spin_unlock(&bdev->fence_lock);
 		if (tmp_obj)
 			driver->sync_obj_unref(&tmp_obj);
+		if (tmp_obj_read)
+			driver->sync_obj_unref(&tmp_obj_read);
+		if (tmp_obj_write)
+			driver->sync_obj_unref(&tmp_obj_write);
 
 		ret = ttm_buffer_object_transfer(bo, &ghost_obj);
 		if (ret)

drivers/gpu/drm/ttm/ttm_bo_vm.c

@@ -122,7 +122,7 @@ static int ttm_bo_vm_fault(struct vm_area_struct *vma, struct vm_fault *vmf)
 
 	spin_lock(&bdev->fence_lock);
 	if (test_bit(TTM_BO_PRIV_FLAG_MOVING, &bo->priv_flags)) {
-		ret = ttm_bo_wait(bo, false, true, false);
+		ret = ttm_bo_wait(bo, false, true, false, TTM_USAGE_READWRITE);
 		spin_unlock(&bdev->fence_lock);
 		if (unlikely(ret != 0)) {
 			retval = (ret != -ERESTARTSYS) ?

drivers/gpu/drm/ttm/ttm_execbuf_util.c

@@ -221,8 +221,18 @@ void ttm_eu_fence_buffer_objects(struct list_head *list, void *sync_obj)
 
 	list_for_each_entry(entry, list, head) {
 		bo = entry->bo;
+		entry->old_sync_obj_read = NULL;
+		entry->old_sync_obj_write = NULL;
 		entry->old_sync_obj = bo->sync_obj;
 		bo->sync_obj = driver->sync_obj_ref(sync_obj);
+		if (entry->usage & TTM_USAGE_READ) {
+			entry->old_sync_obj_read = bo->sync_obj_read;
+			bo->sync_obj_read = driver->sync_obj_ref(sync_obj);
+		}
+		if (entry->usage & TTM_USAGE_WRITE) {
+			entry->old_sync_obj_write = bo->sync_obj_write;
+			bo->sync_obj_write = driver->sync_obj_ref(sync_obj);
+		}
 		bo->sync_obj_arg = entry->new_sync_obj_arg;
 		ttm_bo_unreserve_locked(bo);
 		entry->reserved = false;
@@ -231,8 +241,15 @@ void ttm_eu_fence_buffer_objects(struct list_head *list, void *sync_obj)
 	spin_unlock(&bdev->fence_lock);
 
 	list_for_each_entry(entry, list, head) {
-		if (entry->old_sync_obj)
+		if (entry->old_sync_obj) {
 			driver->sync_obj_unref(&entry->old_sync_obj);
+		}
+		if (entry->old_sync_obj_read) {
+			driver->sync_obj_unref(&entry->old_sync_obj_read);
+		}
+		if (entry->old_sync_obj_write) {
+			driver->sync_obj_unref(&entry->old_sync_obj_write);
+		}
 	}
 }
 EXPORT_SYMBOL(ttm_eu_fence_buffer_objects);

drivers/gpu/drm/vmwgfx/vmwgfx_execbuf.c

@@ -224,6 +224,7 @@ static int vmw_translate_guest_ptr(struct vmw_private *dev_priv,
 	if (unlikely(cur_validate_node == sw_context->cur_val_buf)) {
 		val_buf = &sw_context->val_bufs[cur_validate_node];
 		val_buf->bo = ttm_bo_reference(bo);
+		val_buf->usage = TTM_USAGE_READWRITE;
 		val_buf->new_sync_obj_arg = (void *) dev_priv;
 		list_add_tail(&val_buf->head, &sw_context->validate_nodes);
 		++sw_context->cur_val_buf;

include/drm/ttm/ttm_bo_api.h

@@ -44,6 +44,11 @@ struct ttm_bo_device;
 
 struct drm_mm_node;
 
+enum ttm_buffer_usage {
+    TTM_USAGE_READ = 1,
+    TTM_USAGE_WRITE = 2,
+    TTM_USAGE_READWRITE = TTM_USAGE_READ | TTM_USAGE_WRITE
+};
 
 /**
  * struct ttm_placement
@@ -174,7 +179,10 @@ struct ttm_tt;
  * the bo_device::lru_lock.
  * @reserved: Deadlock-free lock used for synchronization state transitions.
  * @sync_obj_arg: Opaque argument to synchronization object function.
- * @sync_obj: Pointer to a synchronization object.
+ * @sync_obj: Pointer to a synchronization object of a last read or write,
+ * whichever is later.
+ * @sync_obj_read: Pointer to a synchronization object of a last read.
+ * @sync_obj_write: Pointer to a synchronization object of a last write.
  * @priv_flags: Flags describing buffer object internal state.
  * @vm_rb: Rb node for the vm rb tree.
  * @vm_node: Address space manager node.
@@ -258,6 +266,8 @@ struct ttm_buffer_object {
 
 	void *sync_obj_arg;
 	void *sync_obj;
+	void *sync_obj_read;
+	void *sync_obj_write;
 	unsigned long priv_flags;
 
 	/**
@@ -325,6 +335,7 @@ ttm_bo_reference(struct ttm_buffer_object *bo)
  * @bo:  The buffer object.
  * @interruptible:  Use interruptible wait.
  * @no_wait:  Return immediately if buffer is busy.
+ * @usage:  Whether to wait for the last read and/or the last write.
  *
  * This function must be called with the bo::mutex held, and makes
  * sure any previous rendering to the buffer is completed.
@@ -334,7 +345,8 @@ ttm_bo_reference(struct ttm_buffer_object *bo)
  * Returns -ERESTARTSYS if interrupted by a signal.
  */
 extern int ttm_bo_wait(struct ttm_buffer_object *bo, bool lazy,
-		       bool interruptible, bool no_wait);
+		       bool interruptible, bool no_wait,
+		       enum ttm_buffer_usage usage);
 /**
  * ttm_bo_validate
  *

include/drm/ttm/ttm_execbuf_util.h

@@ -41,20 +41,26 @@
  * @bo:             refcounted buffer object pointer.
  * @new_sync_obj_arg: New sync_obj_arg for @bo, to be used once
  * adding a new sync object.
+ * @usage           Indicates how @bo is used by the device.
  * @reserved:       Indicates whether @bo has been reserved for validation.
  * @removed:        Indicates whether @bo has been removed from lru lists.
  * @put_count:      Number of outstanding references on bo::list_kref.
  * @old_sync_obj:   Pointer to a sync object about to be unreferenced
+ * @old_sync_obj_read: Pointer to a read sync object about to be unreferenced.
+ * @old_sync_obj_write: Pointer to a write sync object about to be unreferenced.
  */
 
 struct ttm_validate_buffer {
 	struct list_head head;
 	struct ttm_buffer_object *bo;
 	void *new_sync_obj_arg;
+	enum ttm_buffer_usage usage;
 	bool reserved;
 	bool removed;
 	int put_count;
 	void *old_sync_obj;
+	void *old_sync_obj_read;
+	void *old_sync_obj_write;
 };
 
 /**